1. Field of the Invention
The present invention relates to methods and systems for controlling an actuator to rotate a valve installed in a passage through which gas flows, thereby adjusting an opening area of the passage.
More particularly, the present invention relates to methods and systems are capable of controlling an actuator to control rotation of a valve installed in an exhaust-gas recirculation passage through which part of exhaust gas emitted from an exhaust manifold coupled to each cylinder of an engine is returned into a combustion chamber of the engine. The valve rotation control via the actuator allows an opening area of the exhaust-gas recirculation passage to be adjusted, making it possible to reduce emissions in the exhaust gas.
2. Description of the Related Art
Conventional EGR (Exhaust Gas Recirculation) control systems include a substantially discoid valving element disposed in an exhaust-gas recirculation passage to be rotatable. The rotation of the valving element allows adjustment of an opening area of the exhaust-gas recirculation passage.
The conventional EGR control systems also include an actuator configured to give force to the valving element to rotate it, and include a spring configured to constantly bias the valving element toward the passage closing direction.
The conventional EGR control systems include a seal ring mounted on the outer periphery of the valving element such that the seal ring prevents exhaust gas from leaking toward the inlet side of the engine when the valving element is located close to a fully close position where the passage is fully closed. Moreover, the conventional EGR control systems include a controller operative to provide instructions to the actuator to control the opening and closing of the valving element.
As the actuator, an electric motor is commonly used. When the controller energizes the electric motor via a motor driver, the energized electric motor generates torque so that the generated torque is imparted to the valve shaft to rotate it together with the valving element.
The electric motor can switch the direction of the torque imparted thereby between the passage opening direction and the passage closing direction.
The controller is operative to determine, according to the engine operating conditions, a command position of the valving element that allows the opening of the exhaust-gas recirculation passage to be properly determined depending on the engine operating conditions.
Next, the controller is operative to obtain the deviation between the command position and a current position of the valving element sensed by a position sensor, and to calculate a command value corresponding to the required amount and/or direction of power to be supplied to the electric motor based on the obtained deviation. It is to be noted that the command position of the valving element will be referred to as “target valve position”, and the sensed current position of the valving element will be referred to as “current valve position”.
After the calculation of the command value, control signals are determined by the controller based on the command value corresponding to a required amount and/or direction of power, and the determined control signals are output to the motor driver. The motor driver controls the amount and/or direction of power to be supplied to the electric motor. This allows the current valve position to substantially agree with the target valve position, making it possible to perform the exhaust-gas recirculation depending on the engine operating conditions.
When the force applied to the valving element by the electric motor causes the valving element to rotate toward the target valve position, the valving element is subjected to resistance against the application force. The resistance is the resultant of: biasing force (spring force) of the spring toward the passage closing direction, sliding frictional force of the seal ring against the inner wall of the exhaust-gas recirculation passage, sliding frictional force between the outer periphery of a valve shaft and bearings rotatably supporting the valve shaft, and the like.
The sliding frictional force as the component of the resistance changes with a change in amount of deposits, such as black smoke particles and oil mist particles, these deposits are accumulated between, for example, the inner passage wall and the valving element.
Increase of the sliding friction force due to the accumulation of the deposits requires increase of the application force to the valving element. This may increase the amount of power to be supplied to the electric motor, resulting that stable operation of the electric motor may be difficult.
For this reason, in such conventional EGR control systems, a predetermined upper limit on the amount of power to be fed to the electric motor is determined to maintain stable operation of the electric motor, and is stored in, for example, the controller beforehand. Specifically, if the amount of power supplied to the electric motor reaches the upper limit, the controller halts the supply of power to the electric motor.
In the power supply control, however, the valving element has been subjected to no force for rotating the valving element toward the passage opening direction since the stop of power supply to the electric motor. For this reason, the spring force causes the valving element to be continuously biased in the passage closing direction so that the current valve position coincides with the fully close position. This results in that the exhaust gas is fully transferred to the outlet side of the engine, which may cause emissions in the exhaust gas to significantly increase.
In order to solve the problem due to the stop of power supply to the electric motor, techniques for eliminating the deposits to reduce the sliding friction force have been proposed, which are disclosed in, for example, Japanese Unexamined Patent Publications No. 2001-173464 and No. 2003-314377. These techniques can prevent the power supply to the electric motor from being halted.
The deposit removal operation is executed after it is determined to require the deposit removal operation in any way. This causes a time lag between when it is determined that the deposit removal operation is needed, in other words, when the amount of power supplied to the electric motor approaches the upper limit, and when the deposit removal operation is actually executed.
For this reason, when a large volume of deposits tends to rapidly occur under specific operating conditions of the vehicle, such as under hard acceleration, the amount of power supplied to the electric motor may reach the upper limit during the time-lag. This may cause the supply of power to the electric motor to be halted.